Machines such as excavators, backhoes, front shovels, and the like are used for earthmoving work. These earthmoving machines have work implements which consist primarily of a work bucket linkage. The work bucket linkage is controllably actuated by at least one hydraulic cylinder. An operator typically manipulates the work implement to perform a sequence of distinct functions to load the bucket.
In a typical front-end loader work cycle, the operator first positions the bucket linkage at a pile of material and lowers the bucket downward until the bucket is near the ground surface. Then the operator subsequently raises the bucket through the pile to fill the bucket, and racks or tilts back the bucket to capture the material. The operator backs up the front-end loader from the pile and drives toward a loading receptacle. Finally, the operator dumps the captured load in the loading receptacle and maneuvers the front-end loader back to the pile to begin the work cycle again.
There is an increasing demand in the earthmoving industry to automate the work cycle of a machine such as a front-end loader for several reasons. Unlike a human operator, an automated front-end loader remains consistently productive regardless of environmental conditions and prolonged work hours. The automated front-end loader is ideal for applications where conditions are unsuitable or undesirable for humans. An automated front-end loader also enables more accurate loading and compensates for lack of operator skill.
The major components for autonomous loading, e.g., loading the work implement from a pile of material, recognizing loading receptacle positions and orientations, and loading the material from the work implement into the loading receptacle, are currently under development. All of these functions are typically performed by planning and control system software in computers which output signals to drive servo-actuators on the machine. The planning steps required to determine a strategy for an optimal loading is required. The specific location for removing material from a pile, and the approach of the implement to the excavation start point must be determined so that the loading process is performed as efficiently as possible.
There are systems in the prior art that attempt to automate only specific portions of earthmoving operations, and they typically do not adapt to operation over varying terrain as the excavation progresses. This is primarily because environmental perception in conditions that exist at work sites is a very difficult problem. The most sophisticated earthmoving systems have required the operator to place the bucket at the starting location and a control system takes over the process of filling the bucket, using force and/or joint position feedback to accomplish the task. See, for example, Sameshima, M. and Tozawa, S., "Development of Auto Digging Controller for Construction Machine by Fuzzy Logic Control," In Proc. of Conference Japanese Society of Mechanical Engineers, 1992. At the next level of autonomy are systems that automatically select where to dig. Such systems measure the topology of the terrain using ranging sensors. See, for example, Feng, P. and Yang, Y. and Qi, Z and Sun, S., "Research on Control Method of Planning Level for Excavation Robot," Proc. 9th International Symposium on Automation and Robotics in Construction, Tokyo, 1992. Singh, S., Synthesis of Tactical Plans for Robotic Excavation, Ph.D Thesis, January, 1995, Robotics Institute, Carnegie Mellon University, Pittsburgh, Pa. 15213. Takahashi, H., Damata, H., Masuyama, T., Sarata, S., "Autonomous shoveling of rocks by using image vision system on LHD," In Proc., International Symposium on Mine Mechanization and Automation, June 1995, Golden, Colo. Given the profile of the terrain, optimal digs, or those that maximize excavated volume while minimizing other criteria such as time and energy, are computed. At the highest level of autonomy are proposed systems that sequence the operation of an earthmover over a long period. However, the proposed systems do not disclose means to automate the entire excavation process.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.